Tube end sealing method

ABSTRACT

In a method for closing open ends of tubes, an open tube end is closed using spin-tubing methods known in the art. Following the tube end closing, a concavity is formed in the tube end in a tube end forming machine. The tube end is brazed with the tube end facing upright, so that the braze alloy pools in the concavity, strengthening the tube end.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Patent Application U.S.Ser. No. 62/218,197, entitled “Tube End Sealing Method” and filed onSep. 14, 2015, which is fully incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

Historically, copper tubes have been the industry norm for HVACmanifolds. Aluminum tubing has been gaining acceptance in recent years.However, there are additional challenges in closing the ends of aluminumtubes. Tube ends can be closed via a spin tube operation that is knownin the art. The spin tube operation closes the tube end, but then brazeis applied to strengthen the tube end and make it leak-proof andburst-proof. With copper tubes, when braze material is applied to theclosed tube end, the viscosity of the brazing medium would form a raisedarea, resulting in an adequate thickness and strength of the brazed tubeend.

With aluminum tubes, however, this prior art method is insufficient.That is because the low viscosity of the aluminum braze alloy causes thealloy to flow over the sides of the tube, instead of thickening on theend of the tube as desired. TIG welding can be used to strengthen thealuminum tube ends, but TIG welding requires specialized welders, safetyfeatures and shielding that make it more expensive and time consuming.Brazing is easier than TIG welding and requires no eye protection and noshielding.

The method of the present disclosure solves the problem of closing theend of aluminum tubes by indenting the tube ends after they are spunclosed to form a concave tube end. The concave tube end is then brazed,and the braze alloy collects in the concavity and forms a sufficientthickness to strengthen the tube end adequately.

For purposes of summarizing the invention, certain aspects, advantages,and novel features of the invention have been described herein. It is tobe understood that not necessarily all such advantages may be achievedin accordance with any one particular embodiment of the invention. Thus,the invention may be embodied or carried out in a manner that achievesor optimizes one advantage or group of advantages as taught hereinwithout necessarily achieving other advantages as may be taught orsuggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be better understood with reference to the followingdrawings. The elements of the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the disclosure. Furthermore, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a perspective image of a prior art tube before the tube end isclosed.

FIG. 2 depicts the tube of FIG. 1 after a traditional spin closeoperation has been performed.

FIG. 3 is a cross-sectional image of the tube of FIG. 2.

FIG. 4 depicts a tube end after a traditional TIG weld has been used toreinforce the tube end.

FIG. 5 depicts the tube of FIG. 2 after a concavity has been formed inthe tube end.

FIG. 6 is a cross-sectional image of the tube shown in FIG. 5.

FIG. 7 depicts the tube of FIGS. 5 and 6 following aluminum alloybrazing of the tube end.

FIG. 8 is a cross-sectional image of the tube of FIG. 7.

FIG. 9 depicts exemplary tooling used to form the concavity in a tubeforming machine.

FIG. 10 depicts an exemplary method for forming tube ends using themethod described herein.

FIG. 11 depicts an exemplary concavity tool for forming the concavity inthe tube end.

FIG. 12 depicts a closed tube with a concavity clamped into a fixture inpreparation for brazing.

FIG. 13 depicts two closed tubes with braze rings on the tube ends inpreparation for brazing.

FIG. 14 depicts a tube of FIG. 13 as the braze ring has started to melt.

FIG. 15 depicts the tube of FIG. 14 with the braze completely melted.

DETAILED DESCRIPTION

FIG. 1 is a partial perspective view of a prior art aluminum tube 100,showing an open end 101 of the tube 100 in need of closure.

FIG. 2 depicts the tube 100 after the tube end 101 has been closed via aspin close operation that is known in the art. The spin close operationis generally performed in a tube end closing machine. A bottom closure102 now encloses the open end of the tube 100. However, the bottomclosure is thin and not complete in the center of the tube end 101.

FIG. 3 is a cross section of the tube 100 of FIG. 2. Close examinationreveals that there is a crack 301 near the center of the tube end 101.Cracks similar to this are a normal result from the spin closingtechnique described herein. These cracks can leak and cause the tube tofail under pressure. If the tube 100 were made of copper, brazing theend of copper tubing after a spin close operation generally works wellto reinforce the end of the tube. However, this method doesn't work aswell for aluminum tube ends that have merely been spin-closed. This isbecause the low viscosity of the aluminum brazing alloy causes the alloyto flow over the end of the tube and down the side during the brazingoperation when the braze alloy is molten. In other words, the brazealloy is too thin to build up on the end of the tube and strengthen thebottom closure 102.

The current industry standard is to TIG weld the tube end 101 to make itleak-proof and burst pressure rated. FIG. 4 depicts the tube 100 of FIG.3 after the tube end 101 has been TIG welded. The TIG weld bead 103 isvisible on the tube end 101. TIG welding works to reinforce the tubeend. However, TIG welding is a more expensive and time-consuming processthan aluminum brazing.

FIG. 5 depicts a tube 500 that has been spin-closed using traditionalspin closing methods (i.e., the tube 100 of FIGS. 2 and 3), but in whichthe tube end 501 has been subsequently indented to form a concavity 502in accordance with a method of the present disclosure. In order to formthe concavity 502, the tube end 501 is inserted into an end formingmachine (not shown). A hydraulic ram with a hemispherical end contactsthe tube end and forms the indentation, as further discussed herein.

FIG. 6 is a cross-section of the tube 500 of FIG. 1. (The openings shownin FIGS. 5 and 6 in the tube walls are for manifold tubes that are notrelevant to the present disclosure.) The concavity 502 is formed beforebrazing to allow the braze alloy to pool and form a proper seal on thetube end. For an exemplary 0.750 inch OD tube (with a wall thickness of0.065 inches), the concavity 502 has a depth “d” of about 0.080 inchesand a width “w” of about 0.600 inches. In this example, the concavitywidth “w” extends across 80% of the overall OD of the tube.

FIG. 7 depicts the tube 500 after the aluminum brazing has beenperformed on the tube end 501. The concavity has been filed by braze,which has pooled into the concavity, resulting in a smooth tube end 501.

FIG. 8 depicts a cross-section of the tube 500 of FIG. 7. The wallthickness of the tube end 501 is now generally greater than thethickness of the tube wall (0.065 inches in the exemplary tube discussedabove), and has a thickness “d” at its thickest point of about 0.125 forthe 0.750 OD tube discussed above. Thus the resultant thickness “d” ofthe tube end 501 is at its thickest point 192% of the thickness of thetube wall, or almost twice the thickness of the tube wall.

FIG. 9 depicts exemplary tooling used to form the concavity (not shown)in a tube end forming machine (not shown). A tube 900 is secured by afirst clamp 902 and a second clamp 903, with the tube end 901 extendingfrom the clamps 902 and 903. The clamped tube 900 is held stationary bya tube end forming machine, and a concavity tool 906 is pressed into thetube end 901. The concavity tool 906 comprises a semi-sphericalprotrusion 904 that acts on the tube end 901 to produce the concavity inthe tube end 901. The concavity tool 906 is moved hydraulically in oneembodiment.

FIG. 11 is an enlarged image of the concavity tool 906 of FIG. 9. Theconcavity tool 906 comprises a semi-spherical protrusion 904 extendingfrom a shoulder 920, which extends from a base 921. The protrusion 904has a diameter “r” and an outer diameter “OD.” A straight portion 922adjacent to a semi-spherical portion 923 has a length “l.” In anexemplary embodiment, where the concavity tool is used to create aconcavity in a 0.75 inch OD tube, the concavity tool 906 has dimensionsr of 0.375 inches, OD of 0.750 inches, and l of 0.250 inches.

FIG. 10 depicts an exemplary method 1000 for forming tube ends using themethod described herein. In step 1001 of the method 1000, the tube endis closed using the traditional spin-closing methods discussed herein.One such traditional spin-closing method comprises contacting a toolingmember (spinning disk, not shown) to an open tube end while the tube isstationary, to cause the tube end to close. The tooling member spinsaround the circumference of the tube end and is slowly moved radiallyinwardly until the tube end is closed. This process generally takesplace in a tube end closing machine. The tube is then removed from thetube end closing machine. FIG. 1 depicts the tube before the end isspin-closed using this step, and FIGS. 2 and 3 depict the tube after theend has been spin-closed using this step.

In step 1002 of the method 1000, the concavity tool 906 (FIG. 9)contacts the closed tube end 901 (FIG. 9). The concavity tool 906 has ahemispherical protrusion 904 (FIG. 9) that presses into the tube end 901and forms the concavity. Step 1002 is generally performed in a tube endforming machine, and the tube 900 is removed from the end formingmachine after the concavity is formed.

In step 1003 of the method 1000, the tube end is brazed. In this step,the tube end is directed upwardly so that the braze alloy will pool inthe concavity.

FIGS. 12-15 illustrate the brazing method of step 1003. FIG. 12 depictsan aluminum tube 900 that has been through step 1002 of the method 1000(FIG. 10). The tube 900 is clamped into a fixture 930 such that the tubeend 901 is facing upwards.

FIG. 13 depicts two aluminum tubes 900 a and 900 b clamped into thefixture 930, the fixture 930 configured to retain the tubes 900 a and900 b such that the tube ends are facing upwards. A ring 950 a of brazealloy and flux has been placed on the tube end 901 a of tube 900 a.Similarly, a ring 950 b of braze alloy and flux has been placed on thetube end 901 b of tube 900 b. Two brazing torch heads 951 and 952 aredirected toward tube end 901 a, and two brazing torch heads 953 and 954are directed toward tube end 901 b.

FIG. 14 depicts the torch head 952 beginning to melt the braze ring 950a on tube end 901 a of tube 900 a. FIG. 15 depicts the tube end 901 a oftube 900 a after the braze ring 950 has completely melted and pooled inthe concavity. The ring 950 a of braze and flux is configured tocompletely fill the concavity when it melts. For the 0.750 OD tubeexample discussed herein, 0.5-0.7 grams of braze and flux completelyfills the concavity.

What is claimed is:
 1. A method for closing open ends of aluminum tubes,the method comprising: spin-closing a tube end by contacting a toolingmember to the tube end while the tooling member is spinning; forming aconcavity in the tube end by forcing a hemispherical protrusion into thetube end; brazing the tube end to fill the concavity with aluminum alloybraze.
 2. The method of claim 1, wherein the step of brazing the tubeend to fill the concavity comprises positioning the tube such that thetube end faces upwardly, brazing the tube end and allowing the brazealloy to pool in the concavity.
 3. The method of claim 1, wherein thestep of forming a concavity in the tube end by forcing a hemisphericalprotrusion into the tube end is performed in a tube end forming machine.4. The method of claim 1, wherein the step of spin-closing the tube endby contacting a tooling member to the tube end while the tooling memberis spinning is performed in a tube end closing machine.
 5. The method ofclaim 1, wherein the step of forming a concavity in the tube end resultsin a concavity with a width of substantially 80% of the outer diameterof the tube.
 6. The method of claim 1, wherein the step of forming aconcavity in the tube end results in a concavity with a width of between70% and 90% of the outer diameter of the tube.
 7. The method of claim 1,wherein the step of forming a concavity in the tube end results in aconcavity with a depth of substantially 190% of the wall thickness ofthe tube at the thickest point of the tube end.
 8. The method of claim1, wherein the step of forming a concavity in the tube end results in aconcavity with a depth of between 160% and 200% of the wall thickness ofthe tube at the thickest point of the tube end.
 9. A method forreinforcing closed ends of aluminum tubes, the method comprising:forming a concavity in a tube end by forcing a hemispherical protrusioninto the tube end; and brazing the tube end to fill the concavity. 10.The method of claim 9, wherein the step of brazing the tube end to fillthe concavity comprises positioning the tube such that the tube endfaces upwardly, brazing the tube end, and allowing the braze alloy topool in the concavity.
 11. The method of claim 9, wherein the step offorming a concavity in the tube end by forcing a hemisphericalprotrusion into the tube end is performed in a tube end forming machine.12. The method of claim 9, wherein the step of forming a concavity inthe tube end results in a concavity with a width of substantially 80% ofthe outer diameter of the tube.
 13. The method of claim 9, wherein thestep of forming a concavity in the tube end results in a concavity witha width of between 70% and 90% of the outer diameter of the tube. 14.The method of claim 9, wherein the step of forming a concavity in thetube end results in a concavity with a depth of substantially 190% ofthe wall thickness of the tube at the thickest point of the tube end.15. The method of claim 9, wherein the step of forming a concavity inthe tube end results in a concavity with a depth of between 160% and200% of the wall thickness of the tube at the thickest point of the tubeend.